The present application is a continuation-in-part of U.S. patent application Ser. No. 07/181,432, filed Apr. 14, 1988, entitled Cardiac Defibrillation/Cardioversion Spiral Patch Electrode, and now abandoned.
This invention relates to implantable electrical devices used to terminate or control ventricular or atrial tachyarrhythmias. More specifically, this invention is directed to an implantable defibrillation or cardioversion electrode and a method for placing the electrode on or about the heart to deliver electrical energy to the heart.
It is well known that one technique for arresting ventricular fibrillation is to place two electrodes on the surface of the heart to set up an electrical field between the electrodes when they are pulsed; this electric field eliminates the sporadic electrical charges present on the heart during ventricular fibrillation. The amount of surface area contacted by the electrodes is a major factor in determining how consistently and effectively the developed electric field will affect the fibrillating heart.
Presently, many defibrillation electrodes require major surgical procedures for insertion due to the complex structure of the electrode and the need for precise placement of the electrodes on the heart. These surgical procedures are not only costly to the patient, but raise risks associated with major surgery. There have been attempts to provide simplified placement procedures and lead configurations.
In the pacing field, where the discharge tips are small and the discharge energies are small, electrode design and placement has become quite advanced. For example, U.S. Pat. No. 3,865,118 to Bures and U.S. Pat. No. 3,289,138 to Halvoresen disclose pacing electrodes wherein insulated elongated conductor leads are inserted through an already positioned catheter. Both patents disclose insulated conductors having conductive electrode tips at the ends which spring outwardly to contact the atrial or ventricular walls when the catheter sheath surrounding the leads is removed from the body. The leads themselves are straightened for insertion into the catheter and are preformed to spring in a curved relation to facilitate contact with the heart walls.
In contrast to pacing electrodes, defibrillation/ cardioversion electrodes deliver high discharge energies to the heart tissue (on the order of 20-35 joules, whereas pacing involves only microjoules); and whereas pacing electrodes stimulate the heart at small, localized areas, defibrillation/cardioversion electrodes discharge electrical energy through a major portion (critical mass) of the myocardium. It is for this reason that the defibrillation/cardioversion electrode of today has evolved into the patch electrode with a surface area somewhere in the range of 10 to 30 sq. cm.
The design and deployment of defibrillation/cardioversion electrodes also has evolved and has become more simplified. For example, in U.S. Pat. No. 4,567,900 to Moore, a defibrillator electrode is disclosed comprising a spring wire loop preformed to maintain an oval or circular configuration. Conductive foil extends transversely across the loop and is conductively secured to the loop to form a planar electrode surface. Prior to insertion into a delivery catheter, the wire loop assembly is collapsed to an elongated nonplanar configuration. Once the catheter containing the wire loop electrode is placed into position on the heart within the pericardial space, the catheter is withdrawn and the electrode expands into its planar configuration on the heart. In an alternative form disclosed by Moore, the wire loop is in a flattened coil configuration without the foilized strips.
While the Moore patent teaches the concept of a collapsible wire loop electrode, the method of collapsing and placing the electrode about the heart leaves room for improvement.